Inline documentation for hooks in wp-includes/vars.php.

Props tmtoy, nacin.
Fixes #25466.

Built from https://develop.svn.wordpress.org/trunk@25712


git-svn-id: http://core.svn.wordpress.org/trunk@25625 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Correct phpdoc for wp_check_filetype_and_ext(). props dimadin. fixes #25513.
Built from https://develop.svn.wordpress.org/trunk@25713


git-svn-id: http://core.svn.wordpress.org/trunk@25626 1a063a9b-81f0-0310-95a4-ce76da25c4cd